The Extensible Markup Language (XML) is the standard for data and documents that is finding wide acceptance in the computer industry. XML describes and provides structure to a body of data, such as a file or data packet, referred to herein as a XML entity. The XML standard provides for tags that delimit sections of a XML entity referred to as XML elements. Each XML element may contain one or more name-value pairs referred to as attributes. The following XML Segment A is provided to illustrate XML.
SEGMENT A<book>My book  <publication publisher=”Doubleday”      date=”January”></publication>  <Author>Mark Berry</Author>  <Author>Jane Murray</Author></book>
XML elements are delimited by a start tag and a corresponding end tag. For example, segment A contains the start tag “<Author>” and the end tag “<Author>” to delimit an element. The data between the elements is referred to as the element's content. In the case of this element, the content of the element is the text data ‘Mark Berry.’
Element content may contain various other types of data, which include attributes and other elements. The ‘book’ element is an example of an element that contains one or more elements. Specifically, ‘book’ contains two elements: ‘publication’ and ‘author.’ An element that is contained by another element is referred to as a descendant of that element. Thus, elements ‘publication’ and ‘author’ are descendants of element ‘book.’ An element's attributes are also referred to as being contained by the element.
By defining an element that contains attributes and descendant elements, the XML entity defines a hierarchical tree relationship between the element, its descendant elements, and its attribute. A root node and a set of elements that descend from the root node are referred to herein as a XML document.